In 1984, a small patch, no more than a metre square, of the tropical alga Caulerpa taxifolia was discovered in the Mediterranean – where it had never been seen before – growing on the sea-bed immediately below the Oceanographic Museum of Monaco, then under Jacques Cousteau’s directorship. Five years later, the area of the patch had extended to a hectare. In July 1990, another colony of the same alga appeared at Cap Martin in France, 5 kilometres to the east, and in September of the same year it was found near Toulon, 150 kilometres to the west. In 1992, patches were discovered in the Balearics. By the following year, Caulerpa had spread to Italy, as far as the whirlpool of Scylla and Charybdis, and in 1994 it turned up in the coastal waters of Croatia. By the end of 1996, the alga had invaded and occupied 70 sites on the northern Mediterranean coast, spreading over a total area of more than thirty square kilometres and to a depth of more than a hundred metres.
Alexandre Meinesz, a marine biologist from the University of Nice, had his first encounter with the colony of Caulerpa taxifolia beneath the Oceanographic Museum in the late summer of 1989. The museum employee who first discovered the patch of alga had told a colleague of Meinesz about the discovery, and Meinesz learned of it in early 1988. Meinesz was at first merely curious, and over the following months frequently asked his colleague about the progress of the patch: ‘He knew of my great interest in algae of the order Caulerpales, and he was confident that I would be discreet. I agreed to wait quietly for other news of this introduction of an exotic species.’ The need for discretion is not fully explained. Perhaps somebody’s job at the museum might have been at risk; perhaps a minor scientific coup could be pulled off by whoever first reported the discovery of this oddity. Perhaps it was a naturalist’s inquisitiveness that held Meinesz back: he had devoted much of his research career to the study of these algae, and his first impulse on hearing of a new specimen in unfamiliar surroundings would have been to wait and see what happened; at the very least, he would have wanted to see it for himself. And, though it was certainly odd that a tropical species should survive the cool Mediterranean winters, all his experience of Caulerpa taxifolia – normally a spindly plant that grows sparsely in its native waters – would not have led him to suspect that it could become a rampant invader. Perhaps there were incipient feelings of guilt: Meinesz and some of his colleagues had a few years before recommended the use of Caulerpa for decorative use in aquaria, and aquarium waste is the most likely source of the invasion. Whatever the reason, Meinesz was unprepared for what he would find when he had his first look at the new colony.
Underwater, the sea floor ten metres down appeared blurred and all green despite the good visibility. I tried to distinguish contrasting, relieved surfaces, but everything seemed blanketed in green. I suddenly could not believe my eyes: Caulerpa covered everything. It was magnificent and also very surprising ... Perplexed, I caressed the algae with my outstretched hand. It took me a while to react, my emotion was so great ... The tremendous size of the various parts of the plant was astonishing.
On resurfacing, Meinesz lost no time in telling the Museum directorate of his great concern. He recognised at once that the presence of the alga was abnormal, that it clearly could survive the winter and that it displayed highly invasive properties. The rate of spread of a single patch of Caulerpa taxifolia in the Mediterranean seemed to be about ten metres a year, far outstripping that of the native alga Posidonia oceanica, which advances a mere three metres each century. Most tellingly, Caulerpa was already growing in waters of a range of depths, from surface waters down to at least 30 metres. Its potential to smother the inshore seabed was clear. The response from the directorate, headed by Cousteau’s successor, François Doumenge, was deflating: the alga was beautiful, and since it had colonised barren areas of seabed already severely disturbed by the deposit of thousands of tons of rock and earth from coastal building sites, it was beneficial; and anyway, nothing could be done about it. In a trivial sense, the first two observations were true, though they took no account of Caulerpa’s potential to invade less damaged areas. Ominously, the last point was almost certainly true as well. Five years of discreet inaction had seen to that.
These events are described in the first seven pages of Meinesz’s account. From this point on, he and Doumenge and their detractors and supporters became tangled in a phoney war of information and disinformation, buck-passing and pusillanimity, which occupies the next two hundred depressing pages. The cast is huge, and even Monacan royalty has a bit part: ‘I eat it in doughnuts with the Prince,’ Doumenge has said, as evidence for the benign properties of Caulerpa. Meinesz’s calls for research into its biology in the Mediterranean were dismissed in certain circles – some of them scientific – as an opportunistic ploy to get more funding for his lab. There have even been lawsuits: this translation (by Daniel Simberloff, a professor of ecology at the University of Tennessee, who now heads a multimillion dollar research programme on the biology of invasions) doesn’t include some passages from the French original that were successfully challenged in the courts by Meinesz’s opponents. But for the lack of a triumphant ending or some real violence, this story could have made a subject for a latter-day Tintin adventure: Meinesz the young hero, his colleague Boudouresque a faithful Snowy, Doumenge the villain in his forbidding clifftop citadel, munching Mediterranean laverbread with Prince Rainier and conniving with the sinister Giuseppe Giaccone – an algal specialist at the University of Catania, and also a defrocked priest and former mafioso.
How serious is this invasion? Has it threatened to exterminate any native plants or animals? Is it really a killer, and if it is, how does it kill? And, given that there are depressingly huge numbers of invasive species – an estimated 50,000 in the United States alone – why has a whole book been written about this one? Caulerpa has a degree of toxicity to most native herbivores: given the choice, they will avoid it. But it doesn’t poison ecosystems by releasing toxins, unlike the periodic tides of red algae that bloom naturally in many coastal waters. Where Caulerpa colonises, it excludes other bottom-dwelling plants and animals, and their associated fauna. Although it has not been shown to have led to the extinction of any native species, it has certainly caused local declines and absences, to the alarm of naturalists, fishermen and the tourist trade. Meinesz describes a dive in summer 1992:
I descend towards the depths, where twilight interrupts the darkness for only a few hours. I know that there is a beautiful underwater cliff between 20 and 30 metres ... Multicoloured in the beam of a flashlight, it was magnificent ... Calcareous red algae, and, above all, red and yellow gorgonians were the most visible living elements of this unique ecosystem, where hundreds of species of algae, invertebrates and fishes also lived. Lobsters, moray and conger eels, fork-beards, red corals, and small, beautiful red fishes (cardinal fishes and basslets) also abounded ... Imagine how sad I was to find my cliff now a monotone of green! Cascades of Caulerpa covered everything. Only several tips of the most beautiful gorgonian branches emerged from the green carpet ... The gorgonian larvae ... will no longer choose this hostile environment for their development. The ecosystem has changed.
Control measures have been largely useless. Armies of divers have systematically ripped out colonies of the alga, but this is mercilessly slow: only a couple of square metres per diver per hour can be effectively eradicated, assuming that no small pieces of the alga escape. Sheets of black plastic have been anchored over the prairies of Caulerpa, but the alga simply spreads out from the edges and recolonises the upper surface of the plastic. Many other control measures have been mooted or attempted: herbicides, piles of salt, ultrasound, explosives, scalding, blowtorching, ploughing, smothering with concrete and sand. In every case, no matter how large the team of divers, how determined the authorities or how ingenious the inventor, the alga defeated every method or machine deployed against it.
Probably the only option now is to find an effective biological control agent – a pathogen, parasite or predator that will selectively destroy Caulerpa taxifolia without damaging other marine life. Meinesz reports some encouraging observations with a pair of tropical slugs, Elysia subornata and Oxynoe azuropunctata, that prey on Caulerpa taxifolia but seem to ignore other Mediterranean algae. His team found them by accident in a small consignment of Caribbean Caulerpa in 1993 (and one has to wonder why they hadn’t actively looked for such an agent five years before). The problem was that, unlike Caulerpa, the slugs could not survive the cold winter temperatures of the Mediterranean, and could only reproduce to three or four generations in the warmer months. Meinesz set about getting official backing for a research trial with the slugs. In December 1994, their potential was discussed at a scientific meeting, where many delegates advised caution: biological control agents have in the past become invaders in their own right. A year later, Meinesz and his team wrote to the French Ministry for the Environment, calling for an international audit panel to assess the potential benefits and risks of a field trial with the slugs. A sympathetic official at the Ministry succeeded in having the request submitted to unspecified ‘European authorities’, but the proposal then foundered: the Ministry wasn’t prepared to finance the air fares of the two international experts who would need to visit Nice to make the assessment. After which point, as a handy figleaf for the officials, the Caulerpa apologists from Monaco published an article in a scientific journal, claiming the invasion was a natural event. And there it rested: five years later, there has been no further progress on the only control method that offers the faintest of hopes.
Invaders are now considered second only to habitat destruction as a threat to global biodiversity (and to the economy – invaders are estimated to cost the US more than $100 billion a year). They have been spread effortlessly around the globe, some deliberately (cats, swine, rhododendrons, Caulerpa) and some accidentally as fellow passengers (rats, brown tree snakes which have destroyed the bird life of the island of Guam, Dutch elm disease, the pathogens which went to South America with the conquistadors). The more successful invaders are often hidden from the unspecialised eye, particularly when they’re aquatic. Their spread has been allowed, on the whole, by ignorance and indifference: the case of Caulerpa taxifolia is paradigmatic. It also makes clear why the risks of the potential escape of genes from GM crops with wild relatives need to be quantified.
Invasive species – whether plant or animal – tend to be good dispersers with high reproductive rates, and tolerant of a wide range of ecological conditions. It helps, too, if they can reproduce asexually: Caulerpa taxifolia in the Mediterranean is a single clone: every colony has been established from a small bit of alga which has become detached from a patch elsewhere. Think of the number of pleasure craft and fishing boats dropping and weighing anchor in the Mediterranean, and it’s plain how quickly this can happen. But it is still hard to predict which species will become invasive when transferred to new conditions. Huge numbers have all the characteristics of invaders, yet very few behave as such in their native ecosystems. More progress has been made in understanding which habitats are vulnerable to invasion, and how invasions progress: areas disturbed by humans are prime targets, but so are places where the native biota is defenceless against unfamiliar predators or diseases – ultimately, it seems that nowhere is impregnable, and the only possible check against further invasions would be the enactment and enforcement of international controls.
Probably only in Australia and New Zealand – countries experienced in the control of damage caused by countless invaders – would swift action have been taken. When an alien colony of highly invasive zebra mussels was found to have infested a marina in Darwin a couple of years ago, the authorities closed off the area, quarantined all the boats and dumped chlorine and copper in the water: this killed everything and annoyed the yachters, but the native flora and fauna quickly recolonised and the zebra mussel hasn’t been seen since. Why couldn’t something similar have been done in France? (This case nicely illustrates the point that headline-grabbing one-off pollution disasters, such as the recent oil spill off the Brittany coast or the cyanide spill in the Danube, are often less damaging to ecosystems in the long term than out-of-control biological invaders.)
Frustration pervades this book, and not only for the author. By the end, Meinesz begins to flail. His final chapter, ‘The Three Lessons of Caulerpa’, speaks passionately of the need to preserve biodiversity and to protect it from invaders, but says nothing at all about what could be done to promote more effective responses to invaders in France and in the rest of Europe and the Mediterranean. Instead, he accuses the reductionist sciences, particularly molecular biology, of killing off the science of ecology. It’s certainly true that the emphasis of biology shifted in the second half of the 20th century from whole organisms to cells and molecules, and that there have been worrying losses of expertise in the taxonomic sciences – millions of species are probably still undescribed – which were the foundation of biology in the 19th and early 20th centuries. But it is not true that ecology is in decline: in most Western nations at least, the field has expanded in the past twenty years, whether measured in terms of intellectual achievement or in numbers of researchers and publications. Meinesz remarks that molecular biologists win Nobel Prizes but that there is no Prize for ecology; he neglects to point out that there is another prize – the Crafoord – of similar value that was instituted to fill precisely this (and other) gaps in the Nobel pantheon. There is a tedious tendency within biology, as elsewhere, to denigrate the intellectual value of other subdisciplines. In perpetuating this tendency, Meinesz ignores the fact that the molecular sciences have recently been roped in to answer questions relevant to ecology: the conclusive proof that the invading strain of Caulerpa is a single, genetically uniform clone would not have been possible without molecular biological techniques. If anything, the problems that Meinesz encountered were the legacy of the insularity and weakness in French ecology that persisted until the 1970s, when the determined efforts of a few ecologists and evolutionary biologists helped to engender new, outward-looking academic dynasties that now flourish in Montpellier, Paris and elsewhere. Previously, while ecology had pressed ahead in Scandinavia, Britain, North America and the Antipodes in the 1960s and 1970s, it had remained an afterthought in French biology – and perhaps still was so in the minds of some of the people who stifled Meinesz’s efforts to find out the truth about Caulerpa.
Meinesz is closer to the mark in his analysis of scientific communication and the role of the media. If someone who knows his stuff spots a potential invader, it’s no use waiting for the slow process of peer-reviewed scientific publication to run its course (this occasionally takes a few weeks, but generally months or even years), or relying on the media, as Meinesz came to recognise. The Caulerpa saga – like the current wars over genetically modified foods or mad cows – provides an example of the obfuscating effects of conducting a scientific debate in which the different parties play by different rules. While the alarmist researchers, spearheaded by Meinesz, published many papers in scientific journals in the early 1990s documenting the spread of Caulerpa and its invasive character, the Doumenge camp promulgated their message of its virtues via the columns of Le Provençal and Le Midi Libre. Following the 1997 publication of Meinesz’s book in France, Doumenge sued and – on appeal – won a single franc in exemplary damages. A few months later, the popular science magazine Science et Vie published two articles supporting his position. By the following year, around three hundred papers on the Caulerpa invasion had appeared in the professional literature, and the United Nations Environment Programme had recommended that Mediterranean countries should co-operate in an attempt to counter the threat. At the same time, the French Ministry of the Environment announced – again in Science et Vie – a new research programme on the invasion, involving none of the researchers who had previously studied the alga. It was as if the tortuous events of the ten years since Meinesz first observed Caulerpa beneath the Oceanographic Museum had never happened.